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                <h1 id="常见的设计模式"><a href="#常见的设计模式" class="headerlink" title="常见的设计模式"></a>常见的设计模式</h1><h2 id="一、软件设计的七大原则"><a href="#一、软件设计的七大原则" class="headerlink" title="一、软件设计的七大原则"></a>一、软件设计的七大原则</h2><h3 id="1、开闭原则"><a href="#1、开闭原则" class="headerlink" title="1、开闭原则"></a>1、开闭原则</h3><ul>
<li><strong>定义</strong>：一个软件实体如类、模块和函数应该对扩展开放，对修改关闭。</li>
<li>用抽象构建框架，用实现扩展细节</li>
<li><strong>优点：</strong>提高软件系统的可复用性及可维护性</li>
</ul>
<p><strong>代码演示：</strong></p>
<p>业务场景：对原有的课程进行打折销售</p>
<p>原UML类图：</p>
<p><img src="https://notes-hub.oss-cn-beijing.aliyuncs.com/typora_images/image-20220822173542289.png" alt="image-20220822173542289"></p>
<p>原代码：</p>
<pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">interface</span> <span class="token class-name">ICourse</span> <span class="token punctuation">{</span>
    Integer <span class="token function">getId</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    String <span class="token function">getName</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    Double <span class="token function">getPrice</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre>
<pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">JavaCourse</span> <span class="token keyword">implements</span> <span class="token class-name">ICourse</span><span class="token punctuation">{</span>
    <span class="token keyword">private</span> Integer Id<span class="token punctuation">;</span>
    <span class="token keyword">private</span> String name<span class="token punctuation">;</span>
    <span class="token keyword">private</span> Double price<span class="token punctuation">;</span>

    <span class="token keyword">public</span> <span class="token function">JavaCourse</span><span class="token punctuation">(</span>Integer id<span class="token punctuation">,</span> String name<span class="token punctuation">,</span> Double price<span class="token punctuation">)</span> <span class="token punctuation">{</span>
        Id <span class="token operator">=</span> id<span class="token punctuation">;</span>
        <span class="token keyword">this</span><span class="token punctuation">.</span>name <span class="token operator">=</span> name<span class="token punctuation">;</span>
        <span class="token keyword">this</span><span class="token punctuation">.</span>price <span class="token operator">=</span> price<span class="token punctuation">;</span>
    <span class="token punctuation">}</span>

    <span class="token annotation punctuation">@Override</span>
    <span class="token keyword">public</span> Integer <span class="token function">getId</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token keyword">return</span> <span class="token keyword">this</span><span class="token punctuation">.</span>Id<span class="token punctuation">;</span>
    <span class="token punctuation">}</span>

    <span class="token annotation punctuation">@Override</span>
    <span class="token keyword">public</span> String <span class="token function">getName</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token keyword">return</span> <span class="token keyword">this</span><span class="token punctuation">.</span>name<span class="token punctuation">;</span>
    <span class="token punctuation">}</span>

    <span class="token annotation punctuation">@Override</span>
    <span class="token keyword">public</span> Double <span class="token function">getPrice</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token keyword">return</span> <span class="token keyword">this</span><span class="token punctuation">.</span>price<span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">Test</span> <span class="token punctuation">{</span>
    <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span>String<span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span> <span class="token punctuation">{</span>
        ICourse javaCourse <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">JavaDiscountCourse</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">,</span><span class="token string">"Java教程"</span><span class="token punctuation">,</span><span class="token number">9.9d</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"课程ID："</span><span class="token operator">+</span> javaCourse<span class="token punctuation">.</span><span class="token function">getId</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">+</span> <span class="token string">" 课程名称："</span> <span class="token operator">+</span> javaCourse<span class="token punctuation">.</span><span class="token function">getName</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">+</span> <span class="token string">" 课程价格："</span> <span class="token operator">+</span> javaCourse<span class="token punctuation">.</span><span class="token function">getPrice</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">+</span> <span class="token string">"元"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<p>实现该需求只需新建JavaDiscountCourse继承JavaCourse，且修改Test</p>
<pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">JavaDiscountCourse</span> <span class="token keyword">extends</span> <span class="token class-name">JavaCourse</span><span class="token punctuation">{</span>

    <span class="token keyword">public</span> <span class="token function">JavaDiscountCourse</span><span class="token punctuation">(</span>Integer id<span class="token punctuation">,</span> String name<span class="token punctuation">,</span> Double price<span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token keyword">super</span><span class="token punctuation">(</span>id<span class="token punctuation">,</span> name<span class="token punctuation">,</span> price<span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>

    <span class="token keyword">public</span> Double <span class="token function">getOriginPrice</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
        <span class="token keyword">return</span> <span class="token keyword">super</span><span class="token punctuation">.</span><span class="token function">getPrice</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>

    <span class="token annotation punctuation">@Override</span>
    <span class="token keyword">public</span> Double <span class="token function">getPrice</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token keyword">return</span> <span class="token keyword">super</span><span class="token punctuation">.</span><span class="token function">getPrice</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token operator">*</span><span class="token number">0.8</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">Test</span> <span class="token punctuation">{</span>
    <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span>String<span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span> <span class="token punctuation">{</span>
        ICourse iCourse <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">JavaDiscountCourse</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">,</span><span class="token string">"Java教程"</span><span class="token punctuation">,</span><span class="token number">9.9d</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        JavaDiscountCourse javaCourse <span class="token operator">=</span> <span class="token punctuation">(</span>JavaDiscountCourse<span class="token punctuation">)</span>iCourse<span class="token punctuation">;</span>
        System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"课程ID："</span><span class="token operator">+</span> javaCourse<span class="token punctuation">.</span><span class="token function">getId</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">+</span> <span class="token string">" 课程名称："</span> <span class="token operator">+</span> javaCourse<span class="token punctuation">.</span><span class="token function">getName</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">+</span> <span class="token string">" 课程原价："</span><span class="token operator">+</span> javaCourse<span class="token punctuation">.</span><span class="token function">getOriginPrice</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">+</span> <span class="token string">" 打折后价格："</span> <span class="token operator">+</span> javaCourse<span class="token punctuation">.</span><span class="token function">getPrice</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">+</span> <span class="token string">"元"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<p>修改后的UML类图：</p>
<p><img src="https://notes-hub.oss-cn-beijing.aliyuncs.com/typora_images/image-20220822174211002.png" alt="image-20220822174211002"></p>
<h3 id="2、依赖倒置原则"><a href="#2、依赖倒置原则" class="headerlink" title="2、依赖倒置原则"></a>2、依赖倒置原则</h3><ul>
<li><strong>定义：</strong>高层模块不应该依赖底层模块，二者都应该依赖其抽象</li>
<li>抽象不应该依赖细节；细节应该依赖抽象</li>
<li>针对接口编程，不要针对实现编程</li>
<li>优点：可以减少类间的耦合性、提高系统稳定性，提高代码可读性和可维护性，可降低修改程序所造成的风险</li>
</ul>
<p><strong>代码演示：</strong></p>
<p>原业务：</p>
<pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">Angus</span> <span class="token punctuation">{</span>
    <span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">studyJavaCourse</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
        System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"Angus正在学习Java课程！"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
    <span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">studyFECourse</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
        System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"Angus正在学习前端课程！"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">Test</span> <span class="token punctuation">{</span>
    <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span>String<span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span> <span class="token punctuation">{</span>
        Angus angus <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Angus</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        angus<span class="token punctuation">.</span><span class="token function">studyJavaCourse</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        angus<span class="token punctuation">.</span><span class="token function">studyFECourse</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<p>业务需求：现angus要多学习一门Python课程</p>
<p>改造后：</p>
<pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">interface</span> <span class="token class-name">ICourse</span> <span class="token punctuation">{</span>
    <span class="token keyword">void</span> <span class="token function">studyCourse</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre>
<pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">JavaCourse</span> <span class="token keyword">implements</span> <span class="token class-name">ICourse</span><span class="token punctuation">{</span>
    <span class="token annotation punctuation">@Override</span>
    <span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">studyCourse</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
        System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"Angus正在学习Java课程！"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">FECourse</span> <span class="token keyword">implements</span> <span class="token class-name">ICourse</span><span class="token punctuation">{</span>
    <span class="token annotation punctuation">@Override</span>
    <span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">studyCourse</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
        System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"Angus正在学习前端课程！"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">PythonCourse</span> <span class="token keyword">implements</span> <span class="token class-name">ICourse</span><span class="token punctuation">{</span>
    <span class="token annotation punctuation">@Override</span>
    <span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">studyCourse</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
        System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"Angus正在学习Python课程！"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">Angus</span> <span class="token punctuation">{</span>
    <span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">studyIMoocCourse</span><span class="token punctuation">(</span>ICourse iCourse<span class="token punctuation">)</span><span class="token punctuation">{</span>
        iCourse<span class="token punctuation">.</span><span class="token function">studyCourse</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">Test</span> <span class="token punctuation">{</span>
    <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span>String<span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span> <span class="token punctuation">{</span>
        Angus angus <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Angus</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        angus<span class="token punctuation">.</span><span class="token function">studyIMoocCourse</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">JavaCourse</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        angus<span class="token punctuation">.</span><span class="token function">studyIMoocCourse</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">FECourse</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        angus<span class="token punctuation">.</span><span class="token function">studyIMoocCourse</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">PythonCourse</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<p>UML类图：</p>
<p><img src="https://notes-hub.oss-cn-beijing.aliyuncs.com/typora_images/image-20220823210951550.png" alt="image-20220823210951550"></p>
<h3 id="3、单一职责原则"><a href="#3、单一职责原则" class="headerlink" title="3、单一职责原则"></a>3、单一职责原则</h3><ul>
<li>定义：不要存在多余一个导致类变更的原因</li>
<li>一个类/接口/方法只负责一项职责</li>
<li>优点：降低类的复杂度、提高类的可读性，提高系统的可维护性、降低变更引起的风险</li>
</ul>
<p>代码演示：</p>
<pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">Bird</span> <span class="token punctuation">{</span>
    <span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">mainMoveMode</span><span class="token punctuation">(</span>String birdName<span class="token punctuation">)</span><span class="token punctuation">{</span>
        <span class="token keyword">if</span> <span class="token punctuation">(</span>birdName<span class="token punctuation">.</span><span class="token function">equals</span><span class="token punctuation">(</span><span class="token string">"鸵鸟"</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
            System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>birdName <span class="token operator">+</span> <span class="token string">"用脚走！"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token punctuation">}</span><span class="token keyword">else</span> <span class="token punctuation">{</span>
            System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>birdName <span class="token operator">+</span> <span class="token string">"用翅膀飞！"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token punctuation">}</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">Test</span> <span class="token punctuation">{</span>
    <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span>String<span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span> <span class="token punctuation">{</span>
        Bird bird <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Bird</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        bird<span class="token punctuation">.</span><span class="token function">mainMoveMode</span><span class="token punctuation">(</span><span class="token string">"鸵鸟"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        bird<span class="token punctuation">.</span><span class="token function">mainMoveMode</span><span class="token punctuation">(</span><span class="token string">"大眼"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<p>改造后：</p>
<pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">WalkBird</span> <span class="token punctuation">{</span>
    <span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">mainMoveMode</span><span class="token punctuation">(</span>String birdName<span class="token punctuation">)</span><span class="token punctuation">{</span>
        System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>birdName <span class="token operator">+</span> <span class="token string">"用脚走！"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">FlyBird</span> <span class="token punctuation">{</span>
    <span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">mainMoveBird</span><span class="token punctuation">(</span>String birdName<span class="token punctuation">)</span><span class="token punctuation">{</span>
        System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>birdName <span class="token operator">+</span> <span class="token string">"用翅膀飞！"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">Test</span> <span class="token punctuation">{</span>
    <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span>String<span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span> <span class="token punctuation">{</span>
        WalkBird walkBird <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">WalkBird</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        walkBird<span class="token punctuation">.</span><span class="token function">mainMoveMode</span><span class="token punctuation">(</span><span class="token string">"鸵鸟"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

        FlyBird flyBird <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">FlyBird</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        flyBird<span class="token punctuation">.</span><span class="token function">mainMoveBird</span><span class="token punctuation">(</span><span class="token string">"大雁"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<p>UML类图：</p>
<p><img src="https://notes-hub.oss-cn-beijing.aliyuncs.com/typora_images/image-20220823213410330.png" alt="image-20220823213410330"></p>
<h3 id="4、接口隔离原则"><a href="#4、接口隔离原则" class="headerlink" title="4、接口隔离原则"></a>4、接口隔离原则</h3><ul>
<li>定义：用多个专门的接口，而不使用单一的总接口，客户端不应该依赖它不需要的接口</li>
<li>一个类对一个类的依赖应该建立在最小的接口上</li>
<li>建立单一接口，不要建立庞大臃肿的接口</li>
<li>尽量细化接口，接口中的方法尽量少</li>
<li>注意适度原则，一定要适度</li>
<li>优点：符合我们常说的高内聚低耦合的设计思想，从而使得类具有很好的可读性、可扩展性和可维护性</li>
</ul>
<h3 id="5、迪米特法则（最少知道原则）"><a href="#5、迪米特法则（最少知道原则）" class="headerlink" title="5、迪米特法则（最少知道原则）"></a>5、迪米特法则（最少知道原则）</h3><ul>
<li>一个对象应该对其他对象保持最少的了解。又叫最少知道原则</li>
<li>尽量降低类与类之间的耦合</li>
<li>优点：降低类之间的耦合</li>
<li>强调只和朋友交流，不和陌生人说话<ul>
<li>朋友：出现在成员变量、方法的输入、输出参数中的类称为成员朋友类，而出现在方法体内部的类不属于朋友类</li>
</ul>
</li>
</ul>
<p>代码演示：</p>
<pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">Course</span> <span class="token punctuation">{</span>
<span class="token punctuation">}</span>
</code></pre>
<pre class=" language-java"><code class="language-java"><span class="token keyword">import</span> java<span class="token punctuation">.</span>util<span class="token punctuation">.</span>List<span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">TeamLeader</span> <span class="token punctuation">{</span>
    <span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">checkNumberOfCourse</span><span class="token punctuation">(</span>List<span class="token operator">&lt;</span>Course<span class="token operator">></span> courses<span class="token punctuation">)</span><span class="token punctuation">{</span>
        System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"课程的数量为："</span> <span class="token operator">+</span> courses<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<pre class=" language-java"><code class="language-java"><span class="token keyword">import</span> java<span class="token punctuation">.</span>util<span class="token punctuation">.</span>ArrayList<span class="token punctuation">;</span>
<span class="token keyword">import</span> java<span class="token punctuation">.</span>util<span class="token punctuation">.</span>List<span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">Boss</span> <span class="token punctuation">{</span>

    <span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">commandCheckNumber</span><span class="token punctuation">(</span>TeamLeader teamLeader<span class="token punctuation">)</span><span class="token punctuation">{</span>
        List<span class="token operator">&lt;</span>Course<span class="token operator">></span> courses <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">ArrayList</span><span class="token operator">&lt;</span><span class="token operator">></span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token keyword">int</span> i <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span> i <span class="token operator">&lt;</span> <span class="token number">20</span><span class="token punctuation">;</span> i<span class="token operator">++</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
            courses<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">Course</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token punctuation">}</span>
        teamLeader<span class="token punctuation">.</span><span class="token function">checkNumberOfCourse</span><span class="token punctuation">(</span>courses<span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">Test</span> <span class="token punctuation">{</span>
    <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span>String<span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span> <span class="token punctuation">{</span>
        TeamLeader teamLeader <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">TeamLeader</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        Boss boss <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Boss</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        boss<span class="token punctuation">.</span><span class="token function">commandCheckNumber</span><span class="token punctuation">(</span>teamLeader<span class="token punctuation">)</span><span class="token punctuation">;</span>

    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<p>UML类图：</p>
<p><img src="https://notes-hub.oss-cn-beijing.aliyuncs.com/typora_images/image-20220824211715285.png" alt="image-20220824211715285"></p>
<p>改造后：</p>
<pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">Boss</span> <span class="token punctuation">{</span>
    <span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">commandCheckNumber</span><span class="token punctuation">(</span>TeamLeader teamLeader<span class="token punctuation">)</span><span class="token punctuation">{</span>
        teamLeader<span class="token punctuation">.</span><span class="token function">checkNumberOfCourse</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">TeamLeader</span> <span class="token punctuation">{</span>
    <span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">checkNumberOfCourse</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
        List<span class="token operator">&lt;</span>Course<span class="token operator">></span> courses <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">ArrayList</span><span class="token operator">&lt;</span><span class="token operator">></span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token keyword">int</span> i <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span> i <span class="token operator">&lt;</span> <span class="token number">20</span><span class="token punctuation">;</span> i<span class="token operator">++</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
            courses<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">Course</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token punctuation">}</span>
        System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"课程的数量为："</span> <span class="token operator">+</span> courses<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<p>UML类图：</p>
<p><img src="https://notes-hub.oss-cn-beijing.aliyuncs.com/typora_images/image-20220824212135061.png" alt="image-20220824212135061"></p>
<h2 id="二、工厂模式"><a href="#二、工厂模式" class="headerlink" title="二、工厂模式"></a>二、工厂模式</h2><p>核心本质：</p>
<ul>
<li>实例化对象不使用new，用工厂方法代替</li>
<li>将选择实现类，创建对象统一管理和控制。从而将调用者跟我们的实现类解耦。</li>
</ul>
<h3 id="1、简单工厂模式"><a href="#1、简单工厂模式" class="headerlink" title="1、简单工厂模式"></a>1、简单工厂模式</h3><ul>
<li>定义：由一个工厂对象决定创建出哪一种产品类的实例</li>
<li>类型：创建型，但不属于GOF23种设计模式</li>
</ul>
<h4 id="适用场景"><a href="#适用场景" class="headerlink" title="适用场景"></a>适用场景</h4><ul>
<li>工厂类负责创建的对象比较少</li>
<li>客户端（应用层）只知道传入工厂类的参数，对于如何创建对象（逻辑）不关心</li>
</ul>
<h4 id="优点"><a href="#优点" class="headerlink" title="优点"></a>优点</h4><ul>
<li>只需要传入一个正确的参数，就可以获取你所需要的对象而无需知道其创建细节</li>
</ul>
<h4 id="缺点"><a href="#缺点" class="headerlink" title="缺点"></a>缺点</h4><ul>
<li>工厂类的职责相对过重，增加新的产品需要修改工厂类的判断逻辑，违背开闭原则</li>
</ul>
<h4 id="coding"><a href="#coding" class="headerlink" title="coding"></a>coding</h4><pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">abstract</span> <span class="token keyword">class</span> <span class="token class-name">Video</span> <span class="token punctuation">{</span>
    <span class="token keyword">public</span> <span class="token keyword">abstract</span> <span class="token keyword">void</span> <span class="token function">produce</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre>
<pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">JavaVideo</span> <span class="token keyword">extends</span> <span class="token class-name">Video</span><span class="token punctuation">{</span>
    <span class="token annotation punctuation">@Override</span>
    <span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">produce</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
        System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"录制Java视频课程！"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">PythonVideo</span> <span class="token keyword">extends</span> <span class="token class-name">Video</span><span class="token punctuation">{</span>
    <span class="token annotation punctuation">@Override</span>
    <span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">produce</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
        System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"录制Python视频课程！"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">VideoFactory</span> <span class="token punctuation">{</span>
    <span class="token keyword">public</span> Video <span class="token function">getVideo</span><span class="token punctuation">(</span>Class <span class="token class-name">c</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
        Video video <span class="token operator">=</span> null<span class="token punctuation">;</span>

        <span class="token keyword">try</span> <span class="token punctuation">{</span>
            video <span class="token operator">=</span> <span class="token punctuation">(</span>Video<span class="token punctuation">)</span> Class<span class="token punctuation">.</span><span class="token function">forName</span><span class="token punctuation">(</span>c<span class="token punctuation">.</span><span class="token function">getName</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">newInstance</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token punctuation">}</span> <span class="token keyword">catch</span> <span class="token punctuation">(</span><span class="token class-name">InstantiationException</span> e<span class="token punctuation">)</span> <span class="token punctuation">{</span>
            e<span class="token punctuation">.</span><span class="token function">printStackTrace</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token punctuation">}</span> <span class="token keyword">catch</span> <span class="token punctuation">(</span><span class="token class-name">IllegalAccessException</span> e<span class="token punctuation">)</span> <span class="token punctuation">{</span>
            e<span class="token punctuation">.</span><span class="token function">printStackTrace</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token punctuation">}</span> <span class="token keyword">catch</span> <span class="token punctuation">(</span><span class="token class-name">ClassNotFoundException</span> e<span class="token punctuation">)</span> <span class="token punctuation">{</span>
            e<span class="token punctuation">.</span><span class="token function">printStackTrace</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token punctuation">}</span>
        <span class="token keyword">return</span> video<span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token comment" spellcheck="true">//    public Video getVideo(String type){</span>
<span class="token comment" spellcheck="true">//        if ("java".equalsIgnoreCase(type)){</span>
<span class="token comment" spellcheck="true">//            return new JavaVideo();</span>
<span class="token comment" spellcheck="true">//        }else if("python".equalsIgnoreCase(type)){</span>
<span class="token comment" spellcheck="true">//            return new PythonVideo();</span>
<span class="token comment" spellcheck="true">//        }</span>
<span class="token comment" spellcheck="true">//        return null;</span>
<span class="token comment" spellcheck="true">//    }</span>
<span class="token punctuation">}</span>
</code></pre>
<pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">Test</span> <span class="token punctuation">{</span>
    <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span>String<span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span> <span class="token punctuation">{</span>
        VideoFactory videoFactory <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">VideoFactory</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        Video video <span class="token operator">=</span> videoFactory<span class="token punctuation">.</span><span class="token function">getVideo</span><span class="token punctuation">(</span>JavaVideo<span class="token punctuation">.</span><span class="token keyword">class</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        video<span class="token punctuation">.</span><span class="token function">produce</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment" spellcheck="true">//        VideoFactory videoFactory = new VideoFactory();</span>
<span class="token comment" spellcheck="true">//        Video video = videoFactory.getVideo("java");</span>
<span class="token comment" spellcheck="true">//        if (video == null){</span>
<span class="token comment" spellcheck="true">//            return;</span>
<span class="token comment" spellcheck="true">//        }</span>
<span class="token comment" spellcheck="true">//        video.produce();</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<h4 id="UML类图"><a href="#UML类图" class="headerlink" title="UML类图"></a>UML类图</h4><p><img src="https://notes-hub.oss-cn-beijing.aliyuncs.com/typora_images/image-20220824220947113.png" alt="image-20220824220947113"></p>
<h3 id="2、工厂方法"><a href="#2、工厂方法" class="headerlink" title="2、工厂方法"></a>2、工厂方法</h3><ul>
<li>定义：定义一个创建对象的接口，但是让实现这个接口的类来决定实例化哪个类，工厂方法让类的实例化推迟到子类中进行</li>
<li>类型：创建型</li>
</ul>
<h4 id="适用场景："><a href="#适用场景：" class="headerlink" title="适用场景："></a>适用场景：</h4><ul>
<li><p>创建对象需要大量重复的代码</p>
</li>
<li><p>客户端（应用层）不依赖于产品类实例如何被创建、实现等细节</p>
</li>
<li><p>一个类通过其子类来指定创建哪个对象</p>
</li>
</ul>
<h4 id="优点："><a href="#优点：" class="headerlink" title="优点："></a>优点：</h4><ul>
<li>用户只需要关心所需产品对应的工厂，无需关心创建细节</li>
<li>加入新产品符合开闭原则，提高可扩展性</li>
</ul>
<h4 id="缺点："><a href="#缺点：" class="headerlink" title="缺点："></a>缺点：</h4><ul>
<li>类的个数容易过多，增加复杂度</li>
<li>增加了系统的抽的抽象性和理解难度</li>
</ul>
<h4 id="coding："><a href="#coding：" class="headerlink" title="coding："></a>coding：</h4><pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">abstract</span> <span class="token keyword">class</span> <span class="token class-name">Video</span> <span class="token punctuation">{</span>
    <span class="token keyword">public</span> <span class="token keyword">abstract</span> <span class="token keyword">void</span> <span class="token function">produce</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre>
<pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">JavaVideo</span> <span class="token keyword">extends</span> <span class="token class-name">Video</span><span class="token punctuation">{</span>
    <span class="token annotation punctuation">@Override</span>
    <span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">produce</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
        System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"录制Java视屏..."</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">PythonVideo</span> <span class="token keyword">extends</span> <span class="token class-name">Video</span><span class="token punctuation">{</span>

    <span class="token annotation punctuation">@Override</span>
    <span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">produce</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
        System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"生产Python视屏..."</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">abstract</span> <span class="token keyword">class</span> <span class="token class-name">VideoFactory</span> <span class="token punctuation">{</span>
    <span class="token keyword">public</span> <span class="token keyword">abstract</span> Video <span class="token function">getVideo</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre>
<pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">JavaVideoFactory</span> <span class="token keyword">extends</span> <span class="token class-name">VideoFactory</span><span class="token punctuation">{</span>
    <span class="token annotation punctuation">@Override</span>
    <span class="token keyword">public</span> Video <span class="token function">getVideo</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token keyword">return</span> <span class="token keyword">new</span> <span class="token class-name">JavaVideo</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">PythonVoideoFactory</span> <span class="token keyword">extends</span> <span class="token class-name">VideoFactory</span><span class="token punctuation">{</span>
    <span class="token annotation punctuation">@Override</span>
    <span class="token keyword">public</span> Video <span class="token function">getVideo</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token keyword">return</span> <span class="token keyword">new</span> <span class="token class-name">PythonVideo</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">Test</span> <span class="token punctuation">{</span>
    <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span>String<span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span> <span class="token punctuation">{</span>
        VideoFactory videoFactory <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">JavaVideoFactory</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        Video video <span class="token operator">=</span> videoFactory<span class="token punctuation">.</span><span class="token function">getVideo</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        video<span class="token punctuation">.</span><span class="token function">produce</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<h4 id="源码解读："><a href="#源码解读：" class="headerlink" title="源码解读："></a>源码解读：</h4><p>Collection接口中的iterator()就是一个抽象方法，Collection相当于上述的VideoFactory，ArrayList相当于上述Java/PythonVideoFactoty，抽象产品Iterator接口相当于上述Video，ArrayList里面的Itr相当于Java/PythonVideo</p>
<h3 id="3、抽象工厂"><a href="#3、抽象工厂" class="headerlink" title="3、抽象工厂"></a>3、抽象工厂</h3><ul>
<li>定义：抽象工厂模式提供一个创建一系列相关或相互依赖对象的接口</li>
<li>无需指定它们具体的类</li>
<li>类型：创建型</li>
</ul>
<h4 id="适应场景"><a href="#适应场景" class="headerlink" title="适应场景"></a>适应场景</h4><ul>
<li>客户端（应用层）不依赖于产品类实例如何被创建、实现等细节</li>
<li>强调一系列相关产品的产品对象（属于同一产品族）一起使用创建对象需要大量重复的代码</li>
<li>提供一个产品类的库，所有的产品以同样的接口出现，从而使客户端不依赖于具体实现</li>
</ul>
<h4 id="优点-1"><a href="#优点-1" class="headerlink" title="优点"></a>优点</h4><ul>
<li>具体产品在应用层代码隔离，无需关心创建细节</li>
<li>将一个系列的产品族统一到一起创建</li>
</ul>
<h4 id="缺点-1"><a href="#缺点-1" class="headerlink" title="缺点"></a>缺点</h4><ul>
<li>规定了所有可能被创建的产品集合，产品族中扩展新的产品困难，需要修改抽象工厂的接口</li>
<li>增加了系统的抽象性和理解难度</li>
</ul>
<p><img src="https://notes-hub.oss-cn-beijing.aliyuncs.com/typora_images/image-20220904153829824.png" alt="image-20220904153829824"></p>
<p><img src="https://notes-hub.oss-cn-beijing.aliyuncs.com/typora_images/image-20220904164412529.png" alt="image-20220904164412529"></p>
<h4 id="源码解析"><a href="#源码解析" class="headerlink" title="源码解析"></a>源码解析</h4><p>java.sql包下的Connection接口，Mybatis下的SqlSessionFactory</p>
<h2 id="三、单例模式"><a href="#三、单例模式" class="headerlink" title="三、单例模式"></a>三、单例模式</h2><ul>
<li>定义：保证一个类仅有一个实例，并提供一个全局访问点</li>
<li>类型：创建型</li>
</ul>
<h4 id="适用场景-1"><a href="#适用场景-1" class="headerlink" title="适用场景"></a>适用场景</h4><ul>
<li>想确保任何情况下都绝对只有一个实例</li>
</ul>
<h4 id="优点-2"><a href="#优点-2" class="headerlink" title="优点"></a>优点</h4><ul>
<li>在内存里只有一个实例，减少了内存开销</li>
<li>可以避免对资源的多重占用</li>
<li>设置全局访问点，严格控制访问</li>
</ul>
<p>缺点</p>
<ul>
<li>没有接口，扩展困难</li>
</ul>
<h4 id="重点"><a href="#重点" class="headerlink" title="重点"></a>重点</h4><ul>
<li>私有构造器</li>
<li>线程安全</li>
<li>延迟加载</li>
<li>序列化和反序列化安全</li>
<li>反射</li>
</ul>
<h3 id="1、懒汉式"><a href="#1、懒汉式" class="headerlink" title="1、懒汉式"></a>1、懒汉式</h3><h4 id="基础版"><a href="#基础版" class="headerlink" title="基础版"></a>基础版</h4><pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">LazySingleton</span> <span class="token punctuation">{</span>
    <span class="token keyword">private</span> <span class="token keyword">static</span> LazySingleton lazySingleton <span class="token operator">=</span> null<span class="token punctuation">;</span>
    <span class="token keyword">private</span> <span class="token function">LazySingleton</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>

    <span class="token punctuation">}</span>

    <span class="token keyword">public</span> <span class="token keyword">static</span> LazySingleton <span class="token function">getInstance</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
        <span class="token keyword">synchronized</span> <span class="token punctuation">(</span>LazySingleton<span class="token punctuation">.</span><span class="token keyword">class</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
            <span class="token keyword">if</span> <span class="token punctuation">(</span>lazySingleton<span class="token operator">==</span>null<span class="token punctuation">)</span><span class="token punctuation">{</span>
                lazySingleton <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">LazySingleton</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
            <span class="token punctuation">}</span>
        <span class="token punctuation">}</span>
        <span class="token keyword">return</span> lazySingleton<span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<p>由于锁的是LazySingleton类范围比较广，所以此方法开销较大</p>
<h4 id="双重检查版"><a href="#双重检查版" class="headerlink" title="双重检查版"></a>双重检查版</h4><p><img src="https://notes-hub.oss-cn-beijing.aliyuncs.com/typora_images/image-20220905194914893.png" alt="image-20220905194914893"></p>
<pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">LazySingleton</span> <span class="token punctuation">{</span>
    <span class="token comment" spellcheck="true">/**
     * 多线程的时候，cpu会共享内存，
     * 加上volatile关键字后所有线程都能看到共享线程的最新状态，
     * 保证了内存的可见性，可以禁止重排序
     */</span>

    <span class="token keyword">private</span> <span class="token keyword">volatile</span> <span class="token keyword">static</span> LazySingleton lazySingleton <span class="token operator">=</span> null<span class="token punctuation">;</span>
    <span class="token keyword">private</span> <span class="token function">LazySingleton</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>

    <span class="token punctuation">}</span>

    <span class="token keyword">public</span> <span class="token keyword">static</span> LazySingleton <span class="token function">getInstance</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
        <span class="token keyword">if</span> <span class="token punctuation">(</span>lazySingleton<span class="token operator">==</span>null<span class="token punctuation">)</span><span class="token punctuation">{</span>
            <span class="token keyword">synchronized</span> <span class="token punctuation">(</span>LazySingleton<span class="token punctuation">.</span><span class="token keyword">class</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
                <span class="token keyword">if</span> <span class="token punctuation">(</span>lazySingleton<span class="token operator">==</span>null<span class="token punctuation">)</span><span class="token punctuation">{</span>
                    lazySingleton <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">LazySingleton</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
                <span class="token punctuation">}</span>
            <span class="token punctuation">}</span>
        <span class="token punctuation">}</span>
        <span class="token keyword">return</span> lazySingleton<span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<h4 id="静态内部类版"><a href="#静态内部类版" class="headerlink" title="静态内部类版"></a>静态内部类版</h4><p><img src="https://notes-hub.oss-cn-beijing.aliyuncs.com/typora_images/image-20220905195719381.png" alt="image-20220905195719381"></p>
<pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">LazySingleton</span> <span class="token punctuation">{</span>
    <span class="token keyword">private</span> <span class="token keyword">static</span> <span class="token keyword">class</span> <span class="token class-name">InnerClass</span><span class="token punctuation">{</span>
        <span class="token keyword">private</span> <span class="token keyword">static</span> LazySingleton lazySingleton <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">LazySingleton</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
    <span class="token keyword">private</span> <span class="token function">LazySingleton</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span><span class="token punctuation">}</span>
    <span class="token keyword">public</span> <span class="token keyword">static</span> LazySingleton <span class="token function">getInstance</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
        <span class="token keyword">return</span> InnerClass<span class="token punctuation">.</span>lazySingleton<span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<p>关键在于InnerClass内部类的初始化锁，哪个线程拿到锁就创建</p>
<h3 id="2、饿汉式"><a href="#2、饿汉式" class="headerlink" title="2、饿汉式"></a>2、饿汉式</h3><pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">HungrySingleton</span> <span class="token punctuation">{</span>
    <span class="token comment" spellcheck="true">/**
     * 在类加载的时候就初始化
     */</span>
    <span class="token keyword">private</span> <span class="token keyword">final</span> <span class="token keyword">static</span> HungrySingleton hungrySingleton <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">HungrySingleton</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

    <span class="token keyword">private</span> <span class="token function">HungrySingleton</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span><span class="token punctuation">}</span>
    <span class="token keyword">public</span> <span class="token keyword">static</span> HungrySingleton <span class="token function">getInstance</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
        <span class="token keyword">return</span> hungrySingleton<span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<p>容易造成资源浪费</p>
<h3 id="3、序列化和反序列化破坏单例模式"><a href="#3、序列化和反序列化破坏单例模式" class="headerlink" title="3、序列化和反序列化破坏单例模式"></a>3、序列化和反序列化破坏单例模式</h3><p>以饿汉式为例实现序列化接口</p>
<pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">HungrySingleton</span> <span class="token keyword">implements</span> <span class="token class-name">Serializable</span> <span class="token punctuation">{</span>
    <span class="token comment" spellcheck="true">/**
     * 在类加载的时候就初始化
     */</span>
    <span class="token keyword">private</span> <span class="token keyword">final</span> <span class="token keyword">static</span> HungrySingleton hungrySingleton <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">HungrySingleton</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

    <span class="token keyword">private</span> <span class="token function">HungrySingleton</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span><span class="token punctuation">}</span>
    <span class="token keyword">public</span> <span class="token keyword">static</span> HungrySingleton <span class="token function">getInstance</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
        <span class="token keyword">return</span> hungrySingleton<span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">Test</span> <span class="token punctuation">{</span>
    <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span>String<span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span> <span class="token keyword">throws</span> IOException<span class="token punctuation">,</span> ClassNotFoundException <span class="token punctuation">{</span>
        HungrySingleton instance <span class="token operator">=</span> HungrySingleton<span class="token punctuation">.</span><span class="token function">getInstance</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        ObjectOutputStream oos <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">ObjectOutputStream</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">FileOutputStream</span><span class="token punctuation">(</span><span class="token string">"singleton_file"</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        oos<span class="token punctuation">.</span><span class="token function">writeObject</span><span class="token punctuation">(</span>instance<span class="token punctuation">)</span><span class="token punctuation">;</span>

        File file <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">File</span><span class="token punctuation">(</span><span class="token string">"singleton_file"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        ObjectInputStream ois <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">ObjectInputStream</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">FileInputStream</span><span class="token punctuation">(</span>file<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

        HungrySingleton newInstance <span class="token operator">=</span> <span class="token punctuation">(</span>HungrySingleton<span class="token punctuation">)</span> ois<span class="token punctuation">.</span><span class="token function">readObject</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

        System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>instance<span class="token punctuation">)</span><span class="token punctuation">;</span>
        System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>newInstance<span class="token punctuation">)</span><span class="token punctuation">;</span>
        System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>instance<span class="token operator">==</span>newInstance<span class="token punctuation">)</span><span class="token punctuation">;</span>

    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<p>Test类执行结果：</p>
<p><img src="https://notes-hub.oss-cn-beijing.aliyuncs.com/typora_images/image-20220905202548037.png" alt="image-20220905202548037"></p>
<p>从运行结果可以看出两个对象不是同一个，违背的单例模式的初衷</p>
<h3 id="4、序列化和反序列化破坏单例模式解决方案"><a href="#4、序列化和反序列化破坏单例模式解决方案" class="headerlink" title="4、序列化和反序列化破坏单例模式解决方案"></a>4、序列化和反序列化破坏单例模式解决方案</h3><p>只需在单例的类中加入以下方法</p>
<pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">HungrySingleton</span> <span class="token keyword">implements</span> <span class="token class-name">Serializable</span> <span class="token punctuation">{</span>
    <span class="token comment" spellcheck="true">/**
     * 在类加载的时候就初始化
     */</span>
    <span class="token keyword">private</span> <span class="token keyword">final</span> <span class="token keyword">static</span> HungrySingleton hungrySingleton <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">HungrySingleton</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

    <span class="token keyword">private</span> <span class="token function">HungrySingleton</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span><span class="token punctuation">}</span>
    <span class="token keyword">public</span> <span class="token keyword">static</span> HungrySingleton <span class="token function">getInstance</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
        <span class="token keyword">return</span> hungrySingleton<span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
   <span class="token comment" spellcheck="true">/**
    * 
    */</span>
    <span class="token keyword">private</span> Object <span class="token function">readResolve</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
        <span class="token keyword">return</span> hungrySingleton<span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<p>再次执行Test类，得到结果：</p>
<p><img src="https://notes-hub.oss-cn-beijing.aliyuncs.com/typora_images/image-20220905203030393.png" alt="image-20220905203030393"></p>
<p>可以看到，序列化前后的对象是同一个，符合单例设计模式理念。</p>
<h3 id="5、反射攻击单例模式"><a href="#5、反射攻击单例模式" class="headerlink" title="5、反射攻击单例模式"></a>5、反射攻击单例模式</h3><p>还是以饿汉式为例</p>
<pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">HungrySingleton</span><span class="token punctuation">{</span>
    <span class="token comment" spellcheck="true">/**
     * 在类加载的时候就初始化
     */</span>
    <span class="token keyword">private</span> <span class="token keyword">final</span> <span class="token keyword">static</span> HungrySingleton hungrySingleton <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">HungrySingleton</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

    <span class="token keyword">private</span> <span class="token function">HungrySingleton</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span><span class="token punctuation">}</span>
    <span class="token keyword">public</span> <span class="token keyword">static</span> HungrySingleton <span class="token function">getInstance</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
        <span class="token keyword">return</span> hungrySingleton<span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<p>使用反射攻击单例模式</p>
<pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">Test</span> <span class="token punctuation">{</span>
    <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span>String<span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span> <span class="token keyword">throws</span> NoSuchMethodException<span class="token punctuation">,</span> InvocationTargetException<span class="token punctuation">,</span> InstantiationException<span class="token punctuation">,</span> IllegalAccessException <span class="token punctuation">{</span>
        Class <span class="token class-name">objectClass</span> <span class="token operator">=</span> HungrySingleton<span class="token punctuation">.</span><span class="token keyword">class</span><span class="token punctuation">;</span>
        Constructor constructor <span class="token operator">=</span> objectClass<span class="token punctuation">.</span><span class="token function">getDeclaredConstructor</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

        <span class="token comment" spellcheck="true">//通过反射将私有构造器的权限修改</span>
        constructor<span class="token punctuation">.</span><span class="token function">setAccessible</span><span class="token punctuation">(</span><span class="token boolean">true</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        HungrySingleton instance <span class="token operator">=</span> HungrySingleton<span class="token punctuation">.</span><span class="token function">getInstance</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token comment" spellcheck="true">//通过newInstance方法调用构造器，对象就被实例化出来了</span>
        HungrySingleton newInstance <span class="token operator">=</span> <span class="token punctuation">(</span>HungrySingleton<span class="token punctuation">)</span> constructor<span class="token punctuation">.</span><span class="token function">newInstance</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

        System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>instance<span class="token punctuation">)</span><span class="token punctuation">;</span>
        System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>newInstance<span class="token punctuation">)</span><span class="token punctuation">;</span>
        System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>instance <span class="token operator">==</span> newInstance<span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<p>执行结果</p>
<p><img src="https://notes-hub.oss-cn-beijing.aliyuncs.com/typora_images/image-20220905204626766.png" alt="image-20220905204626766"></p>
<h3 id="6、反射攻击单例模式的防御"><a href="#6、反射攻击单例模式的防御" class="headerlink" title="6、反射攻击单例模式的防御"></a>6、反射攻击单例模式的防御</h3><p>适用场景：只有类加载时创建对象的单例模式才可这样防御，如：饿汉式、静态内部类。</p>
<blockquote>
<p>由于懒汉式不是在类加载时创建对象，所以不适合用此方式防御</p>
</blockquote>
<p>修改单例的私有构造器</p>
<pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">HungrySingleton</span><span class="token punctuation">{</span>
    <span class="token comment" spellcheck="true">/**
     * 在类加载的时候就初始化
     */</span>
    <span class="token keyword">private</span> <span class="token keyword">final</span> <span class="token keyword">static</span> HungrySingleton hungrySingleton <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">HungrySingleton</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

    <span class="token keyword">private</span> <span class="token function">HungrySingleton</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
        <span class="token keyword">if</span> <span class="token punctuation">(</span>hungrySingleton<span class="token operator">!=</span>null<span class="token punctuation">)</span><span class="token punctuation">{</span>
            <span class="token keyword">throw</span> <span class="token keyword">new</span> <span class="token class-name">RuntimeException</span><span class="token punctuation">(</span><span class="token string">"单例构造器禁止反射！"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token punctuation">}</span>
    <span class="token punctuation">}</span>
    <span class="token keyword">public</span> <span class="token keyword">static</span> HungrySingleton <span class="token function">getInstance</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
        <span class="token keyword">return</span> hungrySingleton<span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<p>再次执行5中的Test类：</p>
<p><img src="https://notes-hub.oss-cn-beijing.aliyuncs.com/typora_images/image-20220905205018860.png" alt="image-20220905205018860"></p>
<h2 id="四、代理模式"><a href="#四、代理模式" class="headerlink" title="四、代理模式"></a>四、代理模式</h2><ul>
<li>定义：为其他对象提供一种代理，以控制对这个对象的访问</li>
<li>代理对象在客户端和目标对象之间起到中介的作用</li>
<li>类型：结构型</li>
</ul>
<blockquote>
<p>AOP中before就是租房中介朝你签合同，after就是你向中介水电费结算，增强的目标方法就是你租房子的这个行为</p>
</blockquote>
<h4 id="适用场景-2"><a href="#适用场景-2" class="headerlink" title="适用场景"></a>适用场景</h4><ul>
<li>保护目标对象</li>
<li>增强目标对象</li>
</ul>
<h4 id="优点-3"><a href="#优点-3" class="headerlink" title="优点"></a>优点</h4><ul>
<li>代理模式能将代理对象与真实被调用的目标对象分离</li>
<li>一定程度上降低了系统的耦合度，扩展性好</li>
<li>保护目标对象</li>
<li>增强目标对象</li>
</ul>
<h4 id="缺点-2"><a href="#缺点-2" class="headerlink" title="缺点"></a>缺点</h4><ul>
<li>代理模式会造成系统设计中类的数目增加</li>
<li>在客户端和目标对象增加一个代理对象，会造成请求处理速度变慢</li>
<li>增加系统的复杂度</li>
</ul>
<h4 id="扩展"><a href="#扩展" class="headerlink" title="扩展"></a>扩展</h4><ul>
<li>静态代理</li>
<li>动态代理（无法代理类只能代理接口）</li>
<li>CGLib代理</li>
</ul>
<p><strong>Spring代理选择</strong></p>
<ul>
<li>当Bean有实现接口时，Spring就会用JDK的动态代理</li>
<li>当Bean没有实现接口时，Spring使用CGLib</li>
<li>可以强制使用CGLib<ul>
<li>在Spring配置中加入&lt;aop:aspectj-autoproxy proxy-target-class=”true” /&gt;</li>
</ul>
</li>
</ul>
<p><strong>代理速度对比</strong></p>
<p>JDK动态代理 &gt; CGLib</p>
<h3 id="1、静态代理"><a href="#1、静态代理" class="headerlink" title="1、静态代理"></a>1、静态代理</h3><p>以Spring分库为例</p>
<pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">Order</span> <span class="token punctuation">{</span>
    <span class="token keyword">private</span> Object orderInfo<span class="token punctuation">;</span>
    <span class="token keyword">private</span> Integer userId<span class="token punctuation">;</span>

    <span class="token keyword">public</span> Object <span class="token function">getOrderInfo</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token keyword">return</span> orderInfo<span class="token punctuation">;</span>
    <span class="token punctuation">}</span>

    <span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">setOrderInfo</span><span class="token punctuation">(</span>Object orderInfo<span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token keyword">this</span><span class="token punctuation">.</span>orderInfo <span class="token operator">=</span> orderInfo<span class="token punctuation">;</span>
    <span class="token punctuation">}</span>

    <span class="token keyword">public</span> Integer <span class="token function">getUserId</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token keyword">return</span> userId<span class="token punctuation">;</span>
    <span class="token punctuation">}</span>

    <span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">setUserId</span><span class="token punctuation">(</span>Integer userId<span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token keyword">this</span><span class="token punctuation">.</span>userId <span class="token operator">=</span> userId<span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">interface</span> <span class="token class-name">OrderDao</span> <span class="token punctuation">{</span>
    <span class="token keyword">int</span> <span class="token function">insert</span><span class="token punctuation">(</span>Order order<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre>
<pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">OrderDaoImpl</span> <span class="token keyword">implements</span> <span class="token class-name">OrderDao</span> <span class="token punctuation">{</span>
    <span class="token annotation punctuation">@Override</span>
    <span class="token keyword">public</span> <span class="token keyword">int</span> <span class="token function">insert</span><span class="token punctuation">(</span>Order order<span class="token punctuation">)</span> <span class="token punctuation">{</span>
        System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"OrderDao插入Order信息"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token keyword">return</span> <span class="token number">1</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">interface</span> <span class="token class-name">OrderService</span> <span class="token punctuation">{</span>
    <span class="token keyword">boolean</span> <span class="token function">saveOrder</span><span class="token punctuation">(</span>Order order<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre>
<pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">OrderServiceImpl</span> <span class="token keyword">implements</span> <span class="token class-name">OrderService</span> <span class="token punctuation">{</span>
    <span class="token keyword">private</span> OrderDao orderDao<span class="token punctuation">;</span>
    <span class="token annotation punctuation">@Override</span>
    <span class="token keyword">public</span> <span class="token keyword">boolean</span> <span class="token function">saveOrder</span><span class="token punctuation">(</span>Order order<span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token comment" spellcheck="true">//Spring会自己注入，我们这里为了方便直接new</span>
        orderDao <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">OrderDaoImpl</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"Service调用Dao"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token keyword">return</span> orderDao<span class="token punctuation">.</span><span class="token function">insert</span><span class="token punctuation">(</span>order<span class="token punctuation">)</span><span class="token operator">></span><span class="token number">0</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<p>代理类</p>
<pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">OrderServiceStaticProxy</span> <span class="token punctuation">{</span>
    <span class="token keyword">private</span> OrderService orderService<span class="token punctuation">;</span>

    <span class="token keyword">boolean</span> <span class="token function">saveOrder</span><span class="token punctuation">(</span>Order order<span class="token punctuation">)</span><span class="token punctuation">{</span>
        <span class="token function">beforeMethod</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token comment" spellcheck="true">//这里还是一样为了方便直接new</span>
        OrderService orderService <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">OrderServiceImpl</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        Integer userId <span class="token operator">=</span> order<span class="token punctuation">.</span><span class="token function">getUserId</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token keyword">int</span> dbRouter <span class="token operator">=</span> userId <span class="token operator">%</span> <span class="token number">2</span><span class="token punctuation">;</span>
        System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"静态代理分配到【db"</span><span class="token operator">+</span>dbRouter<span class="token operator">+</span><span class="token string">"】处理数据"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        DataSourceContextHolder<span class="token punctuation">.</span><span class="token function">setDBtype</span><span class="token punctuation">(</span>String<span class="token punctuation">.</span><span class="token function">valueOf</span><span class="token punctuation">(</span>dbRouter<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token function">afterMethod</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token keyword">return</span> orderService<span class="token punctuation">.</span><span class="token function">saveOrder</span><span class="token punctuation">(</span>order<span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>

    <span class="token keyword">private</span> <span class="token keyword">void</span> <span class="token function">beforeMethod</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
        System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"静态代理 before code"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
    <span class="token keyword">private</span> <span class="token keyword">void</span> <span class="token function">afterMethod</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
        System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"静态代理 after code"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">DataSourceContextHolder</span> <span class="token punctuation">{</span>
    <span class="token keyword">private</span> <span class="token keyword">static</span> <span class="token keyword">final</span> ThreadLocal<span class="token operator">&lt;</span>String<span class="token operator">></span> CONTEXT_HOLDER <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">ThreadLocal</span><span class="token operator">&lt;</span><span class="token operator">></span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

    <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">setDBtype</span><span class="token punctuation">(</span>String dBtype<span class="token punctuation">)</span><span class="token punctuation">{</span>
        CONTEXT_HOLDER<span class="token punctuation">.</span><span class="token function">set</span><span class="token punctuation">(</span>dBtype<span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
    <span class="token keyword">public</span> <span class="token keyword">static</span> String <span class="token function">getDBtype</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
        <span class="token keyword">return</span> CONTEXT_HOLDER<span class="token punctuation">.</span><span class="token function">get</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
    <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">clearDBType</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
        CONTEXT_HOLDER<span class="token punctuation">.</span><span class="token function">remove</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">DynamicDataSource</span> <span class="token keyword">extends</span> <span class="token class-name">AbstractRoutingDataSource</span> <span class="token punctuation">{</span>
    <span class="token annotation punctuation">@Override</span>
    <span class="token keyword">protected</span> Object <span class="token function">determineCurrentLookupKey</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token keyword">return</span> DataSourceContextHolder<span class="token punctuation">.</span><span class="token function">getDBtype</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<h3 id="2、动态代理"><a href="#2、动态代理" class="headerlink" title="2、动态代理"></a>2、动态代理</h3>
                
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